The analytical chemistry technique comprising partitioning a sample to be analyzed from a preselected receiving fluid with a membrane is known. The membrane is selected to be permeable to the compound in the sample to be analyzed and the compound then passes into the receiving fluid which can be a gas or a liquid. The receiving fluid can then be flowed to, for example, a gas or liquid chromatograph in order to separate and quantify the permeated compound. The membrane is selected to prevent effective contamination of the receiving fluid with other sample components that would otherwise significantly interfere with quantitation.
An example of this type of membrane assisted analytical chemistry is U. S. Pat. No. 4,257,257 to Dairaku et al. wherein the receiving fluid is a gas and the means to quantify the permeated compound is a gas chromatograph. Dairaku et al. discuss the use of both porous and nonporous membranes.
Another example of this type of membrane assisted analytical chemistry is U.S. Pat. No. 4,529,521 to Cortes et al. wherein the receiving fluid is a liquid and the means to quantify the permeated compound is a liquid chromatograph. Cortes et al. discuss the determination of water-soluble monomers in latex products and do not discuss the situation where the monomer concentration is above its solubility limit.
The present inventors were frustrated when they tried to use the above-mentioned inventions for the determination of monomers during polymerization and synthesis of commercial latex products. The problem occurred when the concentration of the monomer exceeded its solubility limit in the aqueous matrix used for latex production. When the solubility limit is exceeded, then droplets of monomer form in the matrix and the calibration curve for analysis, as shown, for example, in FIG. 3 of Dairaku et al., supra, either (a) becomes flat and the method therefore is unusable due to the fact that above the solubility limit the aqueous phase next to the membrane contains a constant concentration of the monomer; or (b) the calibration curve spikes upward unpredictably and thus the method is therefore unusable due to droplets of monomer coating the membrane with a resulting very high permeation of monomer through the membrane.
The present invention solves this problem by effectively emulsifying the droplets of organic compound in the aqueous matrix using, for example, a surfactant. When this is done, then the calibration curve continues to rise predictably and reproducibly and thus usably in the concentration range above the solubility limit in water of the compound to be analyzed.